1. Field of the Invention
The present invention relates to an insert rotary cutter having at least one indexable cutter insert attached to a forward end of a cutter body thereof.
2. Prior Art
Recently, insert rotary cutters of various types have been employed in milling machines, and cutter inserts having convex rake surfaces for their cutting edges have been developed for use in such rotary cutters. Several such related rotary cutters are shown in FIGS. 1 to 19 of the accompanying drawings in which the same or similar members are designated by the same characters. One such cutter 100 shown in FIGS. 1 to 8 comprises a generally cylindrical cutter body 102 including a forward end 104 and a rearward end, the rearward end being adapted to be fixedly secured to a machine spindle so that the body 102 can be rotated in the direction of the arrow R about an axis X therethrough. The forward end 104, which has a forward end face 106 and a circumferential surface 108, includes a pocket 110 formed therein and opening to the circumferential surface 108 and the forward end face 106. The pocket 110 has a circumferentially facing surface 112 sloping in the circumferential direction opposite to that of rotation of the body 102 away from the forward end face 106. The surface 112 has an insert receiving recess 114 formed therein and opening to both the forward end face 106 and the circumferential surface 108, the bottom face of the recess 114 being disposed parallel to the surface 112. Releasably mounted in the recess 114 is an indexable cutter insert 116 of hard wear resistant material fixed in place by a clamp screw 118.
The insert 116, as best shown in FIGS. 5 to 8, comprises a generally rhombic plate defined by a curved front face 120, a flat rear face 122 disposed generally parallel to the front face 120, and four side faces 124. The front face 120 has a pair of parallel opposed marginal ridges serving as respective main cutting edges 126. Those marginal portions of the front face 120 disposed adjacent and extending along the main cutting edges 126 serve as respective rake surfaces 128 for the main cutting edges 126. Each rake surface 128 is convexly arcuate so that each main cutting edge 126 is convexly arcuate and the thickness of the insert 116 along a respective one of the main cutting edges 126 is the largest at the central portion thereof. Each of the side faces 124 is sloping inwardly in a direction away from the front face 120. Corner marginal ridges of the front face 120 serve as respective corner cutting edges 130. The pair of side faces 124 extending from the main cutting edges 126 toward the rear face 122 serve as flanks 132 for the main cutting edges 126, respectively. The insert 116 is disposed in the recess 114 with the rear face 122 being held in contact with the bottom face thereof in such a manner that one of the main cutting edges 126 is indexed in its working position so as to slightly protrude radially outwardly from the circumferential surface 108, and that a mounting inclination angle E of the insert 116 with respect to the axis X of the body 102 is selected to be positive, each main cutting edge 126 extending along the surface 112.
Another related rotary cutter 100a shown in FIGS. 9 to 13 differs from the aforementioned cutter 100 in that a cutter body 102a has a plurality of, say four, generally radially outwardly-opening pockets 110a formed in a circumferential surface 108 of its forward end 104 and disposed adjacent a forward end face 106 in circumferentially and axially equally spaced relation to one another. Each pocket 110a has a circumferentially facing surface 112a including a recess 114a formed therein and opening to the circumferential surface 108, the surface 112a sloping in the circumferential direction opposite to that of rotation of the body 102a away from the forward end face 106, the bottom face of the recess 114a being disposed parallel to the surface 112a. Releasably mounted in each recess 114a is the same cutter insert 116 as that employed in the aforementioned cutter 100. Each insert 116 is disposed in such a manner that one of the main cutting edges 126 is indexed in its working position so as to slightly protrude radially outwardly from the circumferential surface 108, and that a mounting inclination angle E of each insert 116 with respect to the axis X of the body 102a is selected to be positive, each main cutting edge 126 extending along the surface 112a. The indexed main cutting edges 126 of the four inserts 116 are disposed, as shown in FIGS. 12 and 13, in series axially of the body 102a as viewed in the circumferential direction, so as to be brought into alignment with and pass through a common line L parallel to the axis X of the body 102a when the body 102a is rotated.
Still another related rotary cutter 100b shown in FIGS. 14 to 19 comprises a cutter body 102b having a disk-shaped base portion 140 of a circular cross-section integrally formed therewith at a forward end thereof in coaxial relation thereto. The base portion 140 has a forward axial face 142, a rearward axial face 144 and a circumferential surface 146 lying between the forward and rearward axial faces 142 and 144. The base portion 140 also includes a pair of pockets 110b formed therein in diametrically opposite relation. Each of the pair of pockets 110b has a circumferentially facing surface 112b, one of the surfaces 112b sloping in the circumferential direction opposite to that of rotation of the body 102b away from the forward axial face 142, as shown in FIG. 15, while the other surface ( not shown ) is sloping in the same circumferential direction away from the rearward axial face 144. Formed in each surface 112b is a recess 114b having a bottom face disposed parallel to each surface 112b and opening to the circumferential surface 146, one of the recesses 114b also opening to the forward axial face 142 of the base portion 140 while the other recess ( not shown ) is also opening to the rearward axial face 144 thereof. Releasably mounted in each recess 114b is the same cutter insert 116 as those employed in the aforementioned cutters 100 and 100a. Each insert 116 is disposed in such a manner that one of the main cutting edges 126 is indexed in its working position so as to slightly protrude radially outwardly from the circumferential surface 146 of the base portion 140, one of the corner cutting edges 130 of the insert 116 in the one recess 114b being disposed adjacent the corner defined by the forward axial face 142 and the circumferential surface 146 while one of the corner cutting edges 130 of the other insert 116 in the other recess is disposed adjacent the corner defined by the rearward axial face 144 and the circumferential surface 146, and that mounting inclination angles E of the inserts 116 with respect to the axis X are selected to be positive, respectively, as shown in FIGS. 15 and 19. When the base portion 140 is viewed in the circumferential direction, the two inserts 116 are, as shown in FIG. 18, in series axially of the body 102b so as to cooperate to cut T-shaped grooves or the like in a workpiece W.
In the related art cutters 100, 100a and 100b described above, since the rake surface 128 for the indexed main cutting edge 126 of each insert 116 is convexly arcuate, an included angle of a foremost end of each insert 116 is larger than that of an insert having a flat rake surface, thereby the former insert 116 being superior to the latter in the strength of its foremost end. In addition, it is known that, by virtue of unique cutting behavior due to the convexly arcuate shape of the indexed main cutting edge 126, the former insert 116 has advantageous features that its cutting resistance and cutting heat generated during cutting operation are reduced. Moreover, at the rearward portion of the insert 116 extending rearwardly of the body 102, 102a, 102b from the center of the indexed main cutting edge 126, a tangent angle B, which corresponds to an inclination angle of the indexed main cutting edge of the insert or an axial rake angle, is positive and larger than the mounting inclination angle E, as shown in FIGS. 2, 9 and 15, so that chips are smoothly removed along the rake surface 128.
However, in the related art cutters 100, 100a and 100b described above, since the rake surface 128 along the indexed main cutting edge 126 of each insert 116 is convexly arcuate so as to provide the convexly arcuate main cutting edge 126, a tangent angle T.sub.1 of the rake surface 128 in a plane disposed perpendicular to the indexed main cutting edge 126 and passing through the central portion thereof is positive, as shown in FIG. 7, whilst the tangent angle T.sub.2 of the rake surface 128 in a plane disposed perpendicular to the indexed main cutting edge 126 and passing through the rearward portion thereof is, as shown in FIG. 8, negative. The tangent angles T.sub.1 and T.sub.2 correspond to true rake angles or radial rake angles, as shown in FIGS. 3 and 4, FIGS. 10 and 11, and FIGS. 16 and 17. As a result, the true rake angle at the forward portion of the indexed main cutting edge 126 is positive while the true rake angle at the rearward portion thereof is negative. Therefore, particularly in deep cutting operation, in which the rearward portion of the main cutting edge 126 is used, the related art cutters have the drawback that the cutting resistance is extremely increased.